1. Field of the Invention
The present invention relates to a drawing apparatus, and a method of manufacturing an article.
2. Description of the Related Art
In recent years, with an increase in packing density and miniaturization of semiconductor integrated circuits, the line width of a circuit pattern has become very small, so further miniaturization of a pattern (resist pattern) formed (drawn) on a substrate is required in a lithography process. As one of techniques which achieves such pattern miniaturization, a drawing apparatus (charged particle beam drawing apparatus) which performs drawing on a substrate with a charged particle beam is known.
A multi-charged particle beam drawing apparatus generally focuses a plurality of charged particle beams on a substrate, and moves a stage which holds the substrate and the charged particle beams relative to each other, thereby drawing a pattern on the substrate. Therefore, to draw a fine pattern, it is important to accurately align the substrate and the charged particle beams relative to each other.
In aligning a charged particle beam and a substrate with each other in a drawing apparatus, secondary electrons from an alignment mark set (formed) on the substrate are detected by a detector while the charged particle beam is deflected relative to the alignment mark, thereby obtaining the position of the alignment mark. Note that the range of deflection of each of a plurality of charged particle beams is narrower in a multi-charged particle beam drawing apparatus than in a single-charged particle beam drawing apparatus which performs drawing on a substrate with one charged particle beam. Therefore, if the dimension (deflection distance) of each charged particle beam in the direction in which an alignment mark is measured within the range of deflection of this charged particle beam is smaller than the dimension (width) of the alignment mark in the direction in which it is measured, the alignment mark cannot be measured using one charged particle beam alone. Hence, Japanese Patent Nos. 4026872 and 4327434 propose techniques of measuring alignment marks in drawing apparatuses.
Japanese Patent No. 4026872 discloses a drawing apparatus which measures an alignment mark by simultaneously deflecting a plurality of charged particle beams arrayed in the direction in which the alignment mark is measured. In the drawing apparatus disclosed in Japanese Patent No. 4026872, the interval between charged particle beams in the direction in which the alignment mark is measured is set equal to an integer multiple of the pitch between pattern elements (mark elements) which form the alignment mark. Upon this operation, detection signals (secondary electrons) detected by a detector are combined with each other while a plurality of charged particle beams are simultaneously deflected relative to the alignment mark to reduce the influence of distortion and random noise of the detection signals, thereby accurately measuring the alignment mark.
Also, Japanese Patent No. 4327434 discloses two methods for measuring an alignment mark. The first method serves to detect secondary electrons from an alignment mark by a detector while sequentially deflecting a plurality of charged particle beams in accordance with the property of the alignment mark. In the first method, the effective deflection distance of each charged particle beam in the direction in which the alignment mark is measured is set large, and secondary electrons are individually detected by a detector while the charged particle beams are sequentially deflected relative to the alignment mark, thereby allowing measurement of the alignment mark. The second method serves to measure an alignment mark as the deflection distance of each charged particle beam in the direction in which the alignment mark is measured is set large using a measuring deflector for the alignment mark. In the second method, a measuring deflector for the alignment mark is provided separately from a pattern drawing deflector, thereby allowing measurement of the alignment mark with one charged particle beam alone.
However, the pitch between pattern elements which form the alignment mark, and the interval between charged particle beams in the direction in which the alignment mark is measured are not always equal in periodicity. This is because in a process of manufacturing a device, the alignment mark is commonly used even in an apparatus (for example, an exposure apparatus) other than a drawing apparatus, so the pitch between pattern elements cannot be determined only for the sake of convenience of the drawing apparatus. Therefore, a shift may occur in the relative positional relationship between the charged particle beams and the alignment mark (pattern elements), thus making the two ends (their positions) of each of some pattern elements fall outside the range of deflection of each charged particle beam.
Also, when one pattern element (the positions of its two ends) is measured using at least two charged particle beams, as the number of charged particle beams increases, the effective deflection distance of each charged particle beam increases more than when the pattern element is measured using one charged particle beam alone. Especially when the spot size of the charged particle beam is smaller than the length of the alignment mark in the non-measurement direction, it is necessary to measure a plurality of portions in the non-measurement direction for one pattern element, and obtain their integral, in order to reduce an error due to factors associated with the edge flatness of the pattern elements. This prolongs the measurement time of the alignment mark, thus lowering the throughput of the drawing apparatus.
Also, in the drawing apparatus, due, for example, to manufacturing errors of a charged particle optical system, differences may occur in the incident angles (irradiation angles) or intensities (irradiation intensities) of respective charged particle beams. Therefore, when one pattern element is measured using at least two charged particle beams, distortions or variations may occur in the waveforms of detection signals obtained from respective charged particle beams, thus degrading the measurement accuracy of the alignment mark.
FIG. 9 is a view for explaining measurement of an alignment mark in the related art technique. FIG. 9 shows the positional relationship between five charged particle beams CPa to CPe and two pattern elements PEa and PEb which form the alignment mark in the drawing apparatus, and detection signals (their waveforms) obtained by detecting secondary electrons from the pattern elements PEa and PEb, respectively.
Referring to FIG. 9, two ends (positions) M1 and M1′ of the pattern element PEa fall within the range of deflection of the charged particle beam CPa (a range defined by dotted lines P1 and P2), so the position of the pattern element PEa can be measured by deflecting the charged particle beam CPa. In such a case, compared to the case wherein one pattern element is measured using a plurality of charged particle beams, the number of charged particle beams required for measurement is smaller, and the deflection distance of each charged particle beam is smaller, so the alignment mark can be measured in a shorter time. Also, since one pattern element is measured using one charged particle beam, the position of the pattern element PEa can be accurately measured free from the influence of differences in incident angle and intensity of respective charged particle beams (that is, free from the occurrence of distortions or variations in the waveforms of detection signals).
On the other hand, two ends (positions) M2 and M2′ of the pattern element PEb are positioned across the range of deflection of a charged particle beam PEd (a range defined by dotted lines P4 and P5) and that of a charged particle beam PEe (a range defined by dotted lines P5 and P6). In such a case, the pattern element PEb must be measured while the charged particle beams PEd and PEe are sequentially deflected. This lowers the throughput due to an increase in number of charged particle beams required to measure pattern elements, or the measurement accuracy due to differences in incident angle and intensity of respective charged particle beams.
Note that as disclosed in Japanese Patent No. 4026872, when a plurality of charged particle beams are simultaneously deflected, it is possible to prevent a decrease in throughput due to an increase in number of charged particle beams required to measure pattern elements. However, the pitch between pattern elements and the interval between charged particle beams are not always proportional to each other, as described above. Therefore, detection signals having different waveforms are obtained in accordance with the amount of shift between the irradiation positions of the charged particle beams and the positions of the pattern elements, and an error may occur in the waveform obtained by combining these detection signals with each other, thus degrading the measurement accuracy.
Also, as disclosed in Japanese Patent No. 4327434, when a plurality of charged particle beams are sequentially deflected in accordance with the property of the alignment mark (pattern elements), a detection signal is detected for each charged particle beam, so the measurement accuracy degrades due to neither distortions nor variations of the waveforms of the detection signals. However, because at least two charged particle beams are sequentially deflected relative to the two ends of the pattern element, the effective deflection distance of each charged particle beam increases, so the measurement time of the alignment mark increases, thus lowering the throughput of the drawing apparatus, as described above. Due to differences in incident angle and intensity of respective charged particle beams, distortions or variations may occur in the waveforms of detection signals obtained from these charged particle beams, thus degrading the measurement accuracy of the alignment mark.
Moreover, as disclosed in Japanese Patent No. 4327434, when a measuring deflector for the alignment mark is used, the alignment mark (pattern elements) can be measured using one charged particle beam alone, so neither the throughput nor the measurement accuracy lowers in principle. This leads to degradation in measurement accuracy and rise in cost due to an increase in aberration.